Seiko,
unless you posted this question some months ago I still stumbled into the same unanswered question. My answer would be:
Why don't you simply
1. do a distance transform (in python for example using ndimage.distance_transform_edt explained [here](http://pythonvision.org/basic-tutorial) some way down the page)
2. take the point with the largest distance as center and
3. take the corresponding distance as the radius?
The result should be a fastly computed maximum enclosed circle for all types of polygons.
Or am I wrong somehow?
Greets,
Frank